Spinal stabilization device

ABSTRACT

A connection unit for use in a spinal stabilization device, in one embodiment, includes a longitudinal member having first and second ends, and a flexible section disposed between the first and second ends, the flexible section having at least one groove formed therein, wherein the flexible section is characterized by a cross-sectional profile that is different from that of the first and second ends.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 10/798,014, filed Mar. 10, 2004, entitled “A Methodand Apparatus for Flexible Fixation of a Spine” which is acontinuation-in-part of U.S. patent application Ser. No. 10/728,566,filed on Dec. 5, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and system for stabilizing aspinal column and, more particularly, to a method and system of spinalfixation in which one or more screw type securing members are implantedand fixed into a portion of a patient's spinal column and a longitudinalmember including flexible, semi-rigid rod-like or plate-like structuresof various cross-sections (hereinafter referred to as “rods” or“plates”, respectively) are connected and fixed to the upper ends of thesecuring members to provide stabilization of the spinal column.

2. Description of the Related Art

Degenerative spinal column diseases, such as disc degenerative diseases(DDD), spinal stenosis, spondylolisthesis, and so on, need surgicaloperation if they do not take a turn for the better by conservativemanagement. Typically, spinal decompression is the first surgicalprocedure that is performed. The primary purpose of decompression is toreduce pressure in the spinal canal and on nerve roots located thereinby removing a certain tissue of the spinal column to reduce or eliminatethe pressure and pain caused by the pressure. If the tissue of thespinal column is removed the pain is reduced but the spinal column isweakened. Therefore, fusion surgery (e.g., ALIF, PLIF or posterolateralfusion) is often necessary for spinal stability following thedecompression procedure. However, following the surgical procedure,fusion takes additional time to achieve maximum stability and a spinalfixation device is typically used to support the spinal column until adesired level of fusion is achieved. Depending on a patient's particularcircumstances and condition, a spinal fixation surgery can sometimes beperformed immediately following decompression, without performing thefusion procedure. The fixation surgery is performed in most casesbecause it provides immediate postoperative stability and, if fusionsurgery has also been performed, it provides support of the spine untilsufficient fusion and stability has been achieved.

Conventional methods of spinal fixation utilize a rigid spinal fixationdevice to support an injured spinal part and prevent movement of theinjured part. These conventional spinal fixation devices include: fixingscrews configured to be inserted into the spinal pedicle or sacral ofthe backbone to a predetermined depth and angle, rods or platesconfigured to be positioned adjacent to the injured spinal part, andcoupling elements for connecting and coupling the rods or plates to thefixing screws such that the injured spinal part is supported and held ina relatively fixed position by the rods or plates.

U.S. Pat. No. 6,193,720 discloses a conventional spinal fixation device,in which connection members of a rod or plate type are mounted on theupper ends of at least one or more screws inserted into the spinalpedicle or sacral of the backbone. The connection units, such as therods and plates, are used to stabilize the injured part of the spinalcolumn which has been weakened by decompression. The connection unitsalso prevent further pain and injury to the patient by substantiallyrestraining the movement of the spinal column. However, because theconnection units prevent normal movement of the spinal column, afterprolonged use, the spinal fixation device can cause ill effects, such as“junctional syndrome” (transitional syndrome) or “fusion disease”resulting in further complications and abnormalities associated with thespinal column. In particular, due to the high rigidity of the rods orplates used in conventional fixation devices, the patient's fixed jointsare not allowed to move after the surgical operation, and the movementof the spinal joints located above or under the operated area isincreased. Consequently, such spinal fixation devices cause decreasedmobility of the patient and increased stress and instability to thespinal column joints adjacent to the operated area.

It has been reported that excessive rigid spinal fixation is not helpfulto the fusion process due to load shielding caused by rigid fixation.Thus, trials using load sharing semi-rigid spinal fixation devices havebeen performed to eliminate this problem and assist the bone fusionprocess. For example, U.S. Pat. No. 5,672,175, U.S. Pat. No. 5,540,688,and U.S. Pub No 2001/0037111 disclose dynamic spine stabilizationdevices having flexible designs that permit axial load translation(i.e., along the vertical axis of the spine) for bone fusion promotion.However, because these devices are intended for use following a bonefusion procedure, they are not well-suited for spinal fixation withoutfusion. Thus, in the end result, these devices do not prevent theproblem of rigid fixation resulting from fusion.

To solve the above-described problems associated with rigid fixation,non-fusion technologies have been developed. The Graf band is oneexample of a non-fusion fixation device that is applied afterdecompression without bone fusion. The Graf band is composed of apolyethylene band and pedicle screws to couple the polyethylene band tothe spinal vertebrae requiring stabilization. The primary purpose of theGraf band is to prevent sagittal rotation (flexion instability) of theinjured spinal parts. Thus, it is effective in selected cases but is notappropriate for cases that require greater stability and fixation. See,Kanayama et al, Journal of Neurosurgery 95(1 Suppl):5-10, 2001,Markwalder & Wenger, Acta Neurochrgica 145(3):209-14.). Anothernon-fusion fixation device called “Dynesys” has recently beenintroduced. See Stoll et al, European Spine Journal 11 Suppl 2:S170-8,2002, Schmoelz et. al., J. of Spinal Disorder & Techniques 16(4):418-23,2003. The Dynesys device is similar to the Graf band except it uses apolycarburethane spacer between the screws to maintain the distancebetween the heads of two corresponding pedicle screws and, hence,adjacent vertebrae in which the screws are fixed. Early reports by theinventors of the Dynesys device indicate it has been successful in manycases. However, it has not yet been determined whether the Dynesysdevice can maintain long-term stability with flexibility and durabilityin a controlled study. Because it has polyethylene components andinterfaces, there is a risk of mechanical failure. Furthermore, due tothe mechanical configuration of the device, the surgical techniquerequired to attach the device to the spinal column is complex andcomplicated.

U.S. Pat. Nos. 5,282,863 and 4,748,260 disclose a flexible spinalstabilization system and method using a plastic, non-metallic rod. U.S.patent publication no. 2003/0083657 discloses another example of aflexible spinal stabilization device that uses a flexible elongatemember. These devices are flexible but they are not well-suited forenduring long-term axial loading and stress. Additionally, the degree ofdesired flexibility vs. rigidity may vary from patient to patient. Thedesign of existing flexible fixation devices are not well suited toprovide varying levels of flexibility to provide optimum results foreach individual candidate. For example, U.S. Pat. No. 5,672,175discloses a flexible spinal fixation device which utilizes a flexiblerod made of metal alloy and/or a composite material. Additionally,compression or extension springs are coiled around the rod for thepurpose of providing de-rotation forces on the vertebrae in a desireddirection. However, this patent is primarily concerned with providing aspinal fixation device that permits “relative longitudinal translationalsliding movement along [the] vertical axis” of the spine and neitherteaches nor suggests any particular designs of connection units (e.g.,rods or plates) that can provide various flexibility characteristics.Prior flexible rods such as that mentioned in U.S. Pat. No. 5,672,175typically have solid construction with a relatively small diameter inorder to provide a desired level of flexibility. Because they aretypically very thin to provide suitable flexibility, such prior art rodsare prone to mechanical failure and have been known to break afterimplantation in patients.

Therefore, conventional spinal fixation devices have not provided acomprehensive and balanced solution to the problems associated withcuring spinal diseases. Many of the prior devices are characterized byexcessive rigidity, which leads to the problems discussed above whileothers, though providing some flexibility, are not well-adapted toprovide varying degrees of flexibility. Therefore, there is a need foran improved dynamic spinal fixation device that provides a desired levelof flexibility to the injured parts of the spinal column, while alsoproviding long-term durability and consistent stabilization of thespinal column.

Additionally, in a conventional surgical method for fixing the spinalfixation device to the spinal column, a doctor incises the midline ofthe back to about 10-15 centimeters, and then, dissects and retracts itto both sides. In this way, the doctor performs muscular dissection toexpose the outer part of the facet joint. Next, after the dissection,the doctor finds an entrance point to the spinal pedicle usingradiographic devices (e.g., C-arm flouroscopy), and inserts securingmembers of the spinal fixation device (referred to as “spinal pediclescrews”) into the spinal pedicle. Thereafter, the connection units(e.g., rods or plates) are attached to the upper portions of the pediclescrews in order to provide support and stability to the injured portionof the spinal column. Thus, in conventional spinal fixation procedures,the patient's back is incised about 10˜15 cm, and as a result, the backmuscle, which is important for maintaining the spinal column, is incisedor injured, resulting in significant post-operative pain to the patientand a slow recovery period.

Recently, to reduce patient trauma, a minimally invasive surgicalprocedure has been developed which is capable of performing spinalfixation surgery through a relatively small hole or “window” that iscreated in the patient's back at the location of the surgical procedure.Through the use of an endoscope, or microscope, minimally invasivesurgery allows a much smaller incision of the patient's affected area.Through this smaller incision, two or more securing members (e.g.,pedicle screws) of the spinal fixation device are screwed intorespective spinal pedicle areas using a navigation system. Thereafter,special tools are used to connect the stabilizing members (e.g., rods orplates) of the fixation device to the securing members. Alternatively,or additionally, the surgical procedure may include inserting a stepdilator into the incision and then gradually increasing the diameter ofthe dilator. Thereafter, a tubular retractor is inserted into thedilated area to retract the patient's muscle and provide a visual fieldfor surgery. After establishing this visual field, decompression and, ifdesired, fusion procedures may be performed, followed by a fixationprocedure, which includes the steps of finding the position of thespinal pedicle, inserting pedicle screws into the spinal pedicle, usingan endoscope or a microscope, and securing the stabilization members(e.g., rods or plates) to the pedicle screws in order to stabilize andsupport the weakened spinal column.

One of the most challenging aspects of performing the minimally invasivespinal fixation procedure is locating the entry point for the pediclescrew under endoscopic or microscopic visualization. Usually anatomicallandmarks and/or radiographic devices are used to find the entry point,but clear anatomical relationships are often difficult to identify dueto the confined working space. Additionally, the minimally invasiveprocedure requires that a significant amount of the soft tissue must beremoved to reveal the anatomy of the regions for pedicle screwinsertion. The removal of this soft tissue results in bleeding in theaffected area, thereby adding to the difficulty of finding the correctposition to insert the securing members and causing damage to themuscles and soft tissue surrounding the surgical area. Furthermore,because it is difficult to accurately locate the point of insertion forthe securing members, conventional procedures are unnecessarilytraumatic.

Radiography techniques have been proposed and implemented in an attemptto more accurately and quickly find the position of the spinal pediclein which the securing members will be inserted. However, it is oftendifficult to obtain clear images required for finding the correspondingposition of the spinal pedicle using radiography techniques due toradiographic interference caused by metallic tools and equipment usedduring the surgical operation. Moreover, reading and interpretingradiographic images is a complex task requiring significant training andexpertise. Radiography poses a further problem in that the patient isexposed to significant amounts of radiation.

Although some guidance systems have been developed which guide theinsertion of a pedicle screw to the desired entry point on the spinalpedicle, these prior systems have proven difficult to use and,furthermore, hinder the operation procedure. For example, prior guidancesystems for pedicle screw insertion utilize a long wire that is insertedthrough a guide tube that is inserted through a patient's back muscleand tissue. The location of insertion of the guide tube is determined byradiographic means (e.g., C-arm fluoroscope) and driven until a firstend of the guide tube reaches the desired location on the surface of thepedicle bone. Thereafter, a first end of the guide wire, typically madeof a biocompatible metal material, is inserted into the guide tube andpushed into the pedicle bone, while the opposite end of the wire remainsprotruding out of the patient's back. After the guide wire has beenfixed into the pedicle bone, the guide tube is removed, and a holecentered around the guide wire is dilated and retracted. Finally, apedicle screw having an axial hole or channel configured to receive theguide wire therethrough is guided by the guide wire to the desiredlocation on the pedicle bone, where the pedicle screw is screw-driveninto the pedicle.

Although the concept of the wire guidance system is a good one, inpractice, the guide wire has been very difficult to use. Because it is arelatively long and thin wire, the structural integrity of the guidewire often fails during attempts to drive one end of the wire into thepedicle bone, making the process unnecessarily time-consuming andlaborious. Furthermore, because the wire bends and crimps duringinsertion, it does not provide a smooth and secure anchor for guidingsubsequent tooling and pedicle screws to the entry point on the pedicle.Furthermore, current percutaneous wire guiding systems are used inconjunction with C-arm flouroscopy (or other radiographic device)without direct visualization with the use of an endoscope or microscope.Thus, current wire guidance systems pose a potential risk ofmisplacement or pedicle breakage. Finally, because one end of the wireremains protruding out of the head of the pedicle screw, and thepatient's back, this wire hinders freedom of motion by the surgeon inperforming the various subsequent procedures involved in spinal fixationsurgery. Thus, there is a need to provide an improved guidance system,adaptable for use in minimally invasive pedicle screw fixationprocedures under endoscopic or microscopic visualization, which iseasier to implant into the spinal pedicle and will not hinder subsequentprocedures performed by the surgeon.

As discussed above, existing methods and devices used to cure spinaldiseases are in need of much improvement. Most conventional spinalfixation devices are too rigid and inflexible. This excessive rigiditycauses further abnormalities and diseases of the spine, as well assignificant discomfort to the patient. Although some existing spinalfixation devices do provide some level of flexibility, these devices arenot designed or manufactured so that varying levels of flexibility maybe easily obtained to provide a desired level of flexibility for eachparticular patient. Additionally, prior art devices having flexibleconnection units (e.g., rods or plates) pose a greater risk ofmechanical failure and do not provide long-term durability andstabilization of the spine. Furthermore, existing methods of performingthe spinal fixation procedure are unnecessarily traumatic to the patientdue to the difficulty in finding the precise location of the spinalpedicle or sacral of the backbone where the spinal fixation device willbe secured.

BRIEF SUMMARY OF THE INVENTION

The invention addresses the above and other needs by providing animproved method and system for stabilizing an injured or weakened spinalcolumn.

To overcome the deficiencies of conventional spinal fixation devices, inone embodiment, the inventor of the present invention has invented anovel flexible spinal fixation device with an improved construction anddesign that is durable and provides a desired level of flexibility andstability.

As a result of long-term studies to reduce the operation time requiredfor minimally invasive spinal surgery, to minimize injury to tissuesnear the surgical area, in another embodiment, the invention provides amethod and device for accurately and quickly finding a position of thespinal column in which securing members of the spinal fixation devicewill be inserted. A novel guidance/marking device is used to indicatethe position in the spinal column where the securing members will beinserted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective view of a spinal fixation device inaccordance with one embodiment of the invention.

FIG. 2 illustrates a perspective view of spinal fixation device inaccordance with another embodiment of the invention.

FIG. 3 illustrates an exploded view of the coupling assembly 14 of thepedicle screw 2 of FIGS. 1 and 2, in accordance with one embodiment ofthe invention.

FIG. 4 illustrates a perspective view of a flexible rod connection unitin accordance with one embodiment of the invention.

FIG. 5 illustrates a perspective view of a flexible rod connection unitin accordance with another embodiment of the invention.

FIG. 6 illustrates a perspective view of a flexible rod connection unitin accordance with a further embodiment of the invention.

FIG. 7 illustrates a perspective view of a pre-bent flexible rodconnection unit in accordance with one embodiment of the invention.

FIG. 8 illustrates a perspective, cross-sectional view of a flexibleportion of connection unit in accordance with one embodiment of theinvention.

FIG. 9 illustrates a perspective, cross-sectional view of a flexibleportion of connection unit in accordance with another embodiment of theinvention.

FIG. 10 illustrates a perspective, cross-sectional view of a flexibleportion of connection unit in accordance with a further embodiment ofthe invention.

FIG. 11 illustrates a perspective view of a flexible rod connection unitin accordance with one embodiment of the invention.

FIG. 12A illustrates a perspective view of a flexible connection unithaving one or more spacers in between two end portions, in accordancewith one embodiment of the invention.

FIG. 12B illustrates an exploded view of the flexible connection unit ofFIG. 12A.

FIG. 12C provides a view of the male and female interlocking elements ofthe flexible connection unit of FIGS. 12A and 12B, in accordance withone embodiment of the invention.

FIG. 13 shows a perspective view of a flexible connection unit, inaccordance with a further embodiment of the invention.

FIG. 14 illustrates a perspective view of a spinal fixation device inaccordance with another embodiment of the invention.

FIG. 15 illustrates an exploded view of the spinal fixation device ofFIG. 14.

FIG. 16A shows a perspective view of a flexible plate connection unit inaccordance with one embodiment of the invention.

FIG. 16B illustrates a perspective view of a flexible plate connectionunit in accordance with a further embodiment of the invention.

FIG. 16C shows a side view of the flexible plate connection unit of FIG.16A.

FIG. 16D shows a top view of the flexible plate connection unit of FIG.16A.

FIG. 16E illustrates a side view of the flexible plate connection unitof FIG. 16A having a pre-bent configuration in accordance with a furtherembodiment of the invention.

FIG. 17 is a perspective view of a flexible plate connection unit inaccordance with another embodiment of the invention.

FIG. 18 illustrates a perspective view of a flexible plate connectionunit in accordance with another embodiment of the invention.

FIG. 19 illustrates a perspective view of a hybrid rod-plate connectionunit having a flexible middle portion according to a further embodimentof the present invention.

FIG. 20 is a perspective view of a spinal fixation device that utilizesthe hybrid rod-plate connection unit of FIG. 19.

FIG. 21 illustrates a perspective view of the spinal fixation device ofFIG. 1 after it has been implanted into a patient's spinal column.

FIGS. 22A and 22B provide perspective views of spinal fixation devicesutilizing the plate connection units of FIGS. 16A and 16B, respectively.

FIG. 23A illustrates a perspective view of two pedicle screws insertedinto the pedicles of two adjacent vertebrae at a skewed angle, inaccordance with one embodiment of the invention.

FIG. 23B illustrates a structural view of a coupling assembly of apedicle screw in accordance with one embodiment of the invention.

FIG. 23C provides a perspective view of a slanted stabilizing spacer inaccordance with one embodiment of the invention.

FIG. 23D illustrates a side view of the slanted stabilizing spacer ofFIG. 23C.

FIG. 23E is a top view of the cylindrical head of the pedicle screw ofFIG. 23.

FIG. 24 illustrates a perspective view of a marking and guiding devicein accordance with one embodiment of the invention.

FIG. 25 is an exploded view of the marking and guidance device of FIG.24.

FIG. 26A provides a perspective, cross-section view of a patient's spineafter the marking and guiding device of FIG. 24 has been inserted duringsurgery.

FIG. 26B provides a perspective, cross-section view of a patient's spineas an inner trocar of the marking and guiding device of FIG. 24 is beingremoved.

FIGS. 27A and 27B illustrate perspective views of two embodiments of afiducial pin, respectively.

FIG. 28 is a perspective view of a pushing trocar in accordance with afurther embodiment of the invention.

FIG. 29A illustrates a perspective, cross-sectional view of a patient'sspine as the pushing trocar of FIG. 28 is used to drive a fiducial pininto a designate location of a spinal pedicle, in accordance with oneembodiment of the invention.

FIG. 29B illustrates a perspective, cross-sectional view of a patient'sspine after two fiducial pins have been implanted into two adjacentspinal pedicles, in accordance with one embodiment of the invention.

FIG. 30 is a perspective view of a cannulated awl in accordance with oneembodiment of the invention.

FIG. 31 is a perspective, cross-sectional view of a patient's spine asthe cannulated awl of FIG. 30 is being used to enlarge an entry hole fora pedicle screw, in accordance with one embodiment of the invention.

FIG. 32 provides a perspective view of fiducial pin retrieving device,in accordance with one embodiment of the invention.

FIG. 33 is a perspective view of a pedicle screw having an axialcylindrical cavity for receiving at least a portion of a fiducial pintherein, in accordance with a further embodiment of the invention.

FIG. 34 is a perspective, cross-sectional view of a patient's spineafter one pedicle screw has been implanted into a designated location ofa spinal pedicle, in accordance with one embodiment of the invention.

FIG. 35 is a perspective, cross-sectional view of a patient's spineafter two pedicle screws have been implanted into designated locationsof two adjacent spinal pedicles, in accordance with one embodiment ofthe invention.

FIG. 36A is perspective view of a flexible rod for spinal fixationhaving a spiral groove cut therein, in accordance with one embodiment ofthe present invention.

FIG. 36B provides a cross-sectional view of the flexible rod of FIG.36A, taken along lines B-B of FIG. 36A.

FIG. 37A illustrates a perspective view of a flexible rod for spinalfixation having transverse tunnels within the body of the rod, inaccordance with one embodiment of the invention.

FIG. 37B is a cross-sectional view of the flexible rod of FIG. 37A,taken along lines B-B of FIG. 37A.

FIG. 38A is a perspective view of a flexible rod for spinal fixationhaving a spiral groove cut therein and transverse tunnels in the body ofthe rod, in accordance with a further embodiment of the invention.

FIG. 38B is a top view of the flexible rod of FIG. 38A, from theperspective of lines B-B of FIG. 38A.

FIG. 39A is a perspective view of a flexible rod for spinal fixationhaving transverse tunnels within the body of the rod, in accordance withanother embodiment of the invention.

FIG. 39B is a cross-sectional view of the flexible rod of FIG. 39A,taken along lines B-B of that figure.

FIG. 39C is an alternative cross-sectional view of the flexible rod ofFIG. 39A, taken along lines B-B of that figure, having substantiallyorthogonal transverse tunnels in the body of the rod, in accordance witha further embodiment of the invention.

FIG. 40A illustrates a perspective view of a flexible rod for spinalfixation, in accordance with a further embodiment of the invention.

FIG. 40B illustrates a cross-sectional view of a flexible rod for spinalfixation in accordance with a further embodiment of the invention.

FIG. 41A illustrates a perspective view of a flexible longitudinalmember connection unit in accordance with one embodiment of theinvention.

FIG. 41B illustrates a perspective view of the connection unit of FIG.41A assembled with securing members.

FIG. 41C illustrates a perspective view of a flexible longitudinalmember trimmed to length and assembled with securing members.

FIG. 42A illustrates a side view of a flexible longitudinal memberconnection unit in accordance with a further embodiment of theinvention.

FIG. 42B illustrates a side view of a flexible longitudinal memberconnection unit in accordance with another embodiment of the invention.

FIG. 43A illustrates a side view of a flexible longitudinal memberconnection unit in accordance with another embodiment of the invention.

FIG. 43B illustrates a perspective view of a flexible longitudinalmember connection unit in accordance with another embodiment of theinvention.

FIG. 43C illustrates a side view of a flexible longitudinal memberconnection unit in accordance with another embodiment of the invention.

FIG. 43D illustrates a side view of a flexible longitudinal memberconnection unit in accordance with another embodiment of the invention.

FIG. 44 illustrates a perspective view of a flexible longitudinal memberconnection unit in accordance with a further embodiment of theinvention.

FIG. 45A illustrates a cross-section view of a flexible longitudinalmember connection unit in accordance with an embodiment of theinvention.

FIG. 45B illustrates a cross-section view of a flexible longitudinalmember made of two types of material in accordance with anotherembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is described in detail below with reference to the figureswherein like elements are referenced with like numerals throughout.

FIG. 1 depicts a spinal fixation device in accordance with oneembodiment of the present invention. The spinal fixation device includestwo securing members 2 (designated as 2′ and 2″), and a flexiblefixation rod 4 configured to be received and secured within a couplingassembly 14, as described in further detail below with respect to FIG.3. Each securing member 2 includes a threaded screw-type shaft 10configured to be inserted and screwed into a patient's spinal pedicle.As shown in FIG. 1, the screw-type shaft 10 includes an external spiralscrew thread 12 formed over the length of the shaft 10 and a conical tipat the end of the shaft 10 configured to be inserted into the patient'sspinal column at a designated location. Other known forms of thesecuring member 2 may be used in connection with the present inventionprovided the securing member 2 can be inserted and fixed into the spinalcolumn and securely coupled to the rod 4.

As described above, the spinal fixation device is used for surgicaltreatment of spinal diseases by mounting securing members 2 at desiredpositions in the spinal column. In one embodiment, the rod 4 extendsacross two or more vertebrae of the spinal column and is secured by thesecuring members 2 so as to stabilize movement of the two or morevertebrae.

FIG. 2 illustrates a perspective view of a spinal fixation device inaccordance with a further embodiment of the present invention. Thespinal fixation device of FIG. 2 is similar to the spinal fixationdevice of FIG. 1 except that the rod 4 comprises a flexible middleportion 8 juxtaposed between two rigid end portions 9 of the rod 4.

FIG. 3 provides an exploded view of the securing member 2 of FIGS. 1 and2 illustrating various components of the coupling assembly 14, inaccordance with one embodiment of the invention. As shown in FIG. 3, thecoupling assembly 14 includes: a cylindrical head 16 located at a topend of the screw-type shaft 10, a spiral thread or groove 18 formedalong portions of the inner wall surface of the cylindrical head 16, anda U-shaped seating groove 20 configured to receive the rod 4 therein.The coupling assembly 14 further comprises an outside-threaded nut 22having a spiral thread 24 formed on the outside lateral surface of thenut 22, wherein the spiral thread 24 is configured to mate with theinternal spiral thread 18 of the cylindrical head 16. In a furtherembodiment, the coupling assembly 14 includes a fixing cap 26 configuredto be mounted over a portion of the cylindrical head 16 to cover andprotect the outside-threaded nut 22 and more securely hold rod 4 withinseating groove 20. In one embodiment an inner diameter of the fixing gap26 is configured to securely mate with the outer diameter of thecylindrical head 16. Other methods of securing the fixing cap 26 to thecylindrical head, such as correspondingly located notches and groove(not shown), would be readily apparent to those of skill in the art. Inpreferred embodiments the components and parts of the securing member 2may be made of highly rigid and durable bio-compatible materials suchas: stainless steel, iron steel, titanium or titanium alloy. Suchmaterials are known in the art. As also known in the art, and usedherein, “bio-compatible” materials refers to those materials that willnot cause any adverse chemical or immunological reactions after beingimplanted into a patient's body.

As shown in FIGS. 1 and 2, in preferred embodiments, the rod 4 iscoupled to the securing means 2 by seating the rod 4 horizontally intothe seating groove 20 of the coupling means 14 perpendicularly to thedirection of the length of the threaded shaft 10 of securing member 2.The outside threaded nut 22 is then received and screwed into thecylindrical head 16 above the rod 4 so as to secure the rod 4 in theseating groove 20. The fixing cap 26 is then placed over the cylindricalhead 16 to cover, protect and more firmly secure the components in theinternal cavity of the cylindrical head 16. FIGS. 4-7 illustrateperspective views of various embodiments of a rod 4 that may be used ina fixation device, in accordance with the present invention. FIG. 4illustrates the rod 4 of FIG. 1 wherein the entire rod is made anddesigned to be flexible. In this embodiment, rod 4 comprises a metaltube or pipe having a cylindrical wall 5 of a predefined thickness. Inone embodiment, in order to provide flexibility to the rod 4, thecylindrical wall 5 is cut in a spiral fashion along the length of therod 4 to form spiral cuts or grooves 6. As would be apparent to one ofordinary skill in the art, the width and density of the spiral grooves 6may be adjusted to provide a desired level of flexibility. In oneembodiment, the grooves 6 are formed from very thin spiral cuts orincisions that penetrate through the entire thickness of the cylindricalwall of the rod 4. As known to those skilled in the art, the thicknessand material of the tubular walls 5 also affect the level offlexibility.

In one embodiment, the rod 4 is designed to have a flexibility thatsubstantially equals that of a normal back. Flexibility ranges for anormal back are known by those skilled in the art, and one of ordinaryskill can easily determine a thickness and material of the tubular walls5 and a width and density of the grooves 6 to achieve a desiredflexibility or flexibility range within the range for a normal back.When referring to the grooves 6 herein, the term “density” refers totightness of the spiral grooves 6 or, in other words, the distancebetween adjacent groove lines 6 as shown in FIG. 4, for example.However, it is understood that the present invention is not limited to aparticular, predefined flexibility range. In one embodiment, in additionto having desired lateral flexibility characteristics, the rigidity ofthe rod 4 should be able to endure a vertical axial load applied to thepatient's spinal column along a vertical axis of the spine in a uniformmanner with respect to the rest of the patient's natural spine.

FIG. 5 illustrates the rod 4 of FIG. 2 wherein only a middle portion 8is made and designed to be flexible and two end portions 9 are made tobe rigid. In one embodiment, metal end rings or caps 9′, having nogrooves therein, may be placed over respective ends of the rod 4 of FIG.4 so as make the end portions 9 rigid. The rings or caps 9′ may bepermanently affixed to the ends of the rod 4 using known methods such aspressing and/or welding the metals together. In another embodiment, thespiral groove 6 is only cut along the length of the middle portion 8 andthe end portions 9 comprise the tubular wall 5 without grooves 6.Without the grooves 6, the tubular wall 5, which is made of a rigidmetal or metal hybrid material, exhibits high rigidity.

FIG. 6 illustrates a further embodiment of the rod 4 having multiplesections, two flexible sections 8 interleaved between three rigidsections 9. This embodiment may be used, for example, to stabilize threeadjacent vertebrae with respect to each other, wherein three pediclescrews are fixed to a respective one of the vertebrae and the threerigid sections 9 are connected to a coupling assembly 14 of a respectivepedicle screw 2, as described above with respect to FIG. 3. Each of theflexible sections 8 and rigid sections 9 may be made as described abovewith respect to FIG. 5.

FIG. 7 illustrates another embodiment of the rod 4 having a pre-bentstructure and configuration to conform to and maintain a patient'scurvature of the spine, known as “lordosis,” while stabilizing thespinal column. Generally, a patient's lumbar is in the shape of a ‘C’form, and the structure of the rod 4 is formed to coincide to the normallumbar shape when utilized in the spinal fixation device of FIG. 2, inaccordance with one embodiment of the invention. In one embodiment, thepre-bent rod 4 includes a middle portion 8 that is made and designed tobe flexible interposed between two rigid end portions 9. The middleportion 8 and end portions 9 may be made as described above with respectto FIG. 5. Methods of manufacturing metallic or metallic-hybrid tubularrods of various sizes, lengths and pre-bent configurations arewell-known in the art. Additionally, or alternatively, the pre-bentstructure and design of the rod 4 may offset a skew angle when twoadjacent pedicle screws are not inserted parallel to one another, asdescribed in further detail below with respect to FIG. 23A.

Additional designs and materials used to create a flexible tubular rod 4or flexible middle portion 8 are described below with respect to FIGS.8-10. FIG. 8 illustrates a perspective, cross-sectional view of aflexible tubular rod 4, or rod portion 8 in accordance with oneembodiment of the invention. In this embodiment, the flexible rod 4, 8is made from a first metal tube 5 having a spiral groove 6 cut thereinas described above with respect to FIGS. 4-7. A second tube 30 havingspiral grooves 31 cut therein and having a smaller diameter than thefirst tube 5 is inserted into the cylindrical cavity of the first tube5. In one embodiment, the second tube 30 has spiral grooves 31 which arecut in an opposite spiral direction with respect to the spiral grooves 6cut in the first tube 5, such that the rotational torsioncharacteristics of the second tube 30 offset at least some of therotational torsion characteristics of the first tube 5. The secondflexible tube 30 is inserted into the core of the first tube to providefurther durability and strength to the flexible rod 4, 8. The secondtube 30 may be made of the same or different material than the firsttube 5. In preferred embodiments, the material used to manufacture thefirst and second tubes 5 and 30, respectively, may be any one orcombination of the following exemplary metals: stainless steel, ironsteel, titanium, and titanium alloy.

FIG. 9 illustrates a perspective, cross-sectional view of a flexible rod4, 8 in accordance with a further embodiment of the invention. In thisembodiment, the flexible rod 4, 8 includes an inner core made of ametallic wire 32 comprising a plurality of overlapping thin metallicyarns, such as steel yarns, titanium yams, or titanium-alloy yarns. Thewire 32 is encased by a metal, or metal hybrid, flexible tube 5 havingspiral grooves 6 cut therein, as discussed above. The number andthickness of the metallic yarns in the wire 32 also affects the rigidityand flexibility of the rod 4, 8. By changing the number, thickness ormaterial of the yarns flexibility can be increased or decreased. Thus,the number, thickness and/or material of the metallic yarns in the wire32 can be adjusted to provide a desired rigidity and flexibility inaccordance with a patient's particular needs. Those of ordinary skill inthe art can easily determine the number, thickness and material of theyarns, in conjunction with a given flexibility of the tube 5 in order toachieve a desired rigidity v. flexibility profile for the rod 4, 8.

FIG. 10 shows yet another embodiment of a flexible rod 4 wherein theflexible tube 5 encases a non-metallic, flexible core 34. The core 34may be made from known biocompatible shape memory alloys (e.g.,NITINOL), or biocompatible synthetic materials such as: carbon fiber,Poly Ether Ether Ketone (PEEK), Poly Ether Ketone Ketone Ether Ketone(PEKKEK), or Ultra High Molecular Weight Poly Ethylene (UHMWPE).

FIG. 11 illustrates a perspective view of another embodiment of theflexible rod 35 in which a plurality of metal wires 32, as describedabove with respect to FIG. 9, are interweaved or braided together toform a braided metal wire rod 35. Thus, the braided metal wire rod 35can be made from the same materials as the metal wire 32. In addition tothe variability of the rigidity and flexibility of the wire 32 asexplained above, the rigidity and flexibility of the braided rod 35 canbe further modified to achieve desired characteristics by varying thenumber and thickness of the wires 32 used in the braided structure 35.For example, in order to achieve various flexion levels or ranges withinthe known flexion range of a normal healthy spine, those of ordinaryskill in the art can easily manufacture various designs of the braidedwire rod 35 by varying and measuring the flexion provided by differentgauges, numbers and materials of the wire used to create the braidedwire rod 35. In a further embodiment each end of the braided metal wirerod 35 is encased by a rigid metal cap or ring 9′ as described abovewith respect to FIGS. 5-7, to provide a rod 4 having a flexible middleportion 8 and rigid end portions 9. In a further embodiment (not shown),the metal braided wire rod 35 may be utilized as a flexible inner coreencased by a metal tube 5 having spiral grooves 6 cut therein to createa flexible metal rod 4 or rod portion 8, in a similar fashion to theembodiments shown in FIGS. 8-10. As used herein the term “braid” or“braided structure” encompasses two or more wires, strips, strands,ribbons and/or other shapes of material interwoven in an overlappingfashion. Various methods of interweaving wires, strips, strands, ribbonsand/or other shapes of material are known in the art. Such interweavingtechniques are encompassed by the present invention. In anotherexemplary embodiment (not shown), the flexible metal rod 35 includes abraided metal structure having two or more metal strips, strands orribbons interweaved in a diagonally overlapping pattern.

FIG. 12A illustrates a further embodiment of a flexible connection unit36 having two rigid end portions 9′ and an exemplary number of rigidspacers 37. In one embodiment, the rigid end portions 9′ and spacers canbe made of bio-compatible metal or metal-hybrid materials as discussedabove. The connection unit 36 further includes a flexible wire 32, asdiscussed above with respect to FIG. 9′, which traverses an axial cavityor hole (not shown) in each of the rigid end portions 9′ and spacers 37.FIG. 12B illustrates an exploded view of the connection unit 36 thatfurther shows how the wire 32 is inserted through center axis holes ofthe rigid end portions 9′ and spacers 37. As further shown in FIG. 12B,each of the end portions 9′ and spacers 37 include a male interlockingmember 38 which is configured to mate with a female interlocking cavity(not shown) in the immediately adjacent end portion 9′ or spacer 37.FIG. 12C illustrates an exploded side view and indicates with dashedlines the location and configuration of the female interlocking cavity39 for receiving corresponding male interlocking members 38.

FIG. 13 shows a perspective view of a flexible connection unit 40 inaccordance with another embodiment of the invention. The connection 40is similar to the connection unit 36 described above, however, thespacers 42 are configured to have the same shape and design as the rigidend portions 9′. Additionally, the end portions 9′ have an exit hole orgroove 44 located on a lateral side surface through which the wire 32may exit, be pulled taut, and clamped or secured using a metal clip (notshown) or other known techniques. In this way, the length of theflexible connection unit 36 or 40 may be varied at the time of surgeryto fit each patient's unique anatomical characteristics. In oneembodiment, the wire 32 may be secured using a metallic clip or stopper(not shown). For example, a clip or stopper may include a small tubularcylinder having an inner diameter that is slightly larger than thediameter of the wire 32 to allow the wire 32 to pass therethrough. Afterthe wire 32 is pulled to a desired tension through the tubular stopper,the stopper is compressed so as to pinch the wire 32 contained therein.Alternatively, the wire 32 may be pre-secured using known techniquesduring the manufacture of the connection units 36, 40 having apredetermined number of spacers 37, 42 therein.

FIG. 14 depicts a spinal fixation device according to another embodimentof the present invention. The spinal fixation device includes: at leasttwo securing members 2 containing an elongate screw type shaft 10 havingan external spiral thread 12, and a coupling assembly 14. The devicefurther includes a plate connection unit 50, or simply “plate 50,”configured to be securely connected to the coupling parts 14 of the twosecuring members 2. The plate 50 comprises two rigid connection members51 each having a planar surface and joined to each other by a flexiblemiddle portion 8. The flexible middle portion 8 may be made inaccordance with any of the embodiments described above with respect toFIGS. 4-11. Each connection member 51 contains a coupling hole 52configured to receive therethrough a second threaded shaft 54 (FIG. 15)of the coupling assembly 14.

As shown in FIG. 15, the coupling assembly 14 of the securing member 2includes a bolt head 56 adjoining the top of the first threaded shaft 10and having a circumference or diameter greater than the circumference ofthe first threaded shaft 10. The second threaded shaft 54 extendsupwardly from the bolt head 56. The coupling assembly 14 furtherincludes a nut 58 having an internal screw thread configured to matewith the second threaded shaft 54, and one or more washers 60, forclamping the connection member 51 against the top surface of the bolthead 56, thereby securely attaching the plate 50 to the pedicle screw 2.

FIGS. 16A and 16B illustrate two embodiments of a plate connection unit40 having at least two coupling members 51 and at least one flexibleportion 8 interposed between and attached to two adjacent connectionmembers 51. As shown in FIGS. 16A and 16B, the flexible middle portion 8comprises a flexible metal braided wire structure 36 as described abovewith respect to FIG. 11. However, the flexible portion 8 can be designedand manufactured in accordance with any of the embodiments describedabove with respect to FIGS. 4-11, or combinations thereof. FIGS. 16C and16D illustrate a side view and top view, respectively, of the plate 50of FIG. 16A. The manufacture of different embodiments of the flexibleconnection units 50 and 58 having different types of flexible middleportions 8, as described above, is easily accomplished using knownmetallurgical, organic polymer, natural resin, or composite materials,and compatible manufacturing and machining processes.

FIG. 16E illustrate a side view of a pre-bent plate connection unit 50′,in accordance with a further embodiment of the invention. This plateconnection unit 50′ is similar to the plate 50 except that connectionmembers 51′ are formed or bent at an angle θ from a parallel plane 53during manufacture of the plate connection unit 50′. As discussed abovewith respect to the pre-bent rod-like connection unit 4 of FIG. 7, thispre-bent configuration is designed to emulate and support a naturalcurvature of the spine (e.g., lordosis). Additionally, or alternatively,this pre-bent structure may offset a skew angle when two adjacentpedicle screws are not inserted parallel to one another, as described infurther detail below with respect to FIG. 23A.

FIG. 17 illustrates a perspective view of a plate connection unit 60having two planar connection members 62 each having a coupling hole 64therein for receiving the second threaded shaft 44 of the pedicle screw2. A flexible middle portion 8 is interposed between the two connectionmembers 62 and attached thereto. In one embodiment, the flexible middleportion 8 is made in a similar fashion to wire 32 described above withrespect to FIG. 9, except it has a rectangular configuration instead ofa cylindrical or circular configuration as shown in FIG. 9. It isunderstood, however, that the flexible middle portion 8 may be made inaccordance with the design and materials of any of the embodimentspreviously discussed.

FIG. 18 illustrates a perspective view of a further embodiment of theplate 60 of FIG. 17 wherein the coupling hole 64 includes one or morenut guide grooves 66 cut into the top portion of the connection member62 to seat and fix the nut 58 (FIG. 15) into the coupling hole 64. Thenut guide groove 66 is configured to receive and hold at least a portionof the nut 58 therein and prevent lateral sliding of the nut 58 withinthe coupling hole 64 after the connection member 62 has been clamped tothe bolt head 56 of the pedicle screw 2.

FIG. 19 illustrates a perspective view of a hybrid plate and rodconnection unit 70 having a rigid rod-like connection member 4, 9 or 9′,as described above with respect to FIGS. 4-7, at one end of theconnection unit 70 and a plate-like connection member 51 or 62, asdescribed above with respect to FIGS. 14-18, at the other end of theconnection unit 70. In one embodiment, interposed between rod-likeconnection member 9 (9′) and the plate-like connection member 52 (64) isa flexible member 8. The flexible member 8 may be designed andmanufactured in accordance with any of the embodiments discussed abovewith reference to FIGS. 8-13.

FIG. 20 illustrates a perspective view of a spinal fixation device thatutilizes the hybrid plate and rod connection unit 70 of FIG. 19. Asshown in FIG. 20, this fixation device utilizes two types of securingmembers 2 (e.g., pedicle screws), the first securing member 2′ beingconfigured to securely hold the plate connection member 42(64) asdescribed above with respect to FIG. 15, and the second securing member2″ being configured to securely hold the rod connection member 4, 9 or9′, as described above with respect to FIG. 3.

FIG. 21 illustrates a perspective top view of two spinal fixationdevices, in accordance with the embodiment illustrated in FIG. 1, afterthey are attached to two adjacent vertebrae 80 and 82 to flexiblystabilize the vertebrae. FIGS. 22A and 22B illustrate perspective topviews of spinal fixation devices using the flexible stabilizing members50 and 58 of FIGS. 16A and 16B, respectively, after they are attached totwo or more adjacent vertebrae of the spine.

FIG. 23A illustrates a side view of a spinal fixation device after ithas been implanted into the pedicles of two adjacent vertebrae. As shownin this figure, the pedicle screws 2 are mounted into the pedicle bonesuch that a center axis 80 of the screws 2 are offset by an angle θ froma parallel plane 82 and the center axes 80 of the two screws 2 areoffset by an angle of approximately 2θ from each other. This type ofnon-parallel insertion of the pedicle screws 2 often results due to thelimited amount of space that is available when performing minimallyinvasive surgery. Additionally, the pedicle screws 2 may have a tendencyto be skewed from parallel due to a patient's natural curvature of thespine (e.g., lordosis). Thus, due to the non-parallel nature of how thepedicle screws 2 are ultimately fixed to the spinal pedicle, it isdesirable to offset this skew when attaching a rod or plate connectionunit to each of the pedicle screws 2.

FIG. 23B illustrates a side view of the head of the pedicle screw inaccordance with one embodiment of the invention. The screw 2 includes acylindrical head 84 which is similar to the cylindrical head 16described above with respect to FIG. 3 except that the cylindrical head84 includes a slanted seat 86 configured to receive and hold a flexiblerod 4 in a slanted orientation that offsets the slant or skew 0 of thepedicle screw 2 as described above. The improved pedicle screw 2 furtherincludes a slanted stabilizing spacer 88 which is configured to securelyfit inside the cavity of the cylindrical head 84 and hold down the rod 4at the same slant as the slanted seat 86. The pedicle screw 2 furtherincludes an outside threaded nut 22 configured to mate with spiralthreads along the interior surface (not shown) of the cylindrical head84 for clamping down and securing the slanted spacer 88 and the rod 4 tothe slanted seat 86 and, hence, to the cylindrical head 84 of thepedicle screw 2.

FIG. 23C shows a perspective view of the slanted spacer 88, inaccordance with embodiment of the invention. The spacer 88 includes acircular middle portion 90 and two rectangular-shaped end portions 92extending outwardly from opposite sides of the circular middle portion90. FIG. 23D shows a side view of the spacer 88 that further illustratesthe slant from one end to another to compensate or offset the skew angleθ of the pedicle screw 2.

FIG. 23E illustrates a top view of the cylindrical head 84 configured toreceive a rod 4 and slanted spacer 88 therein. The rod 4 is receivedthrough two openings or slots 94 in the cylindrical walls of thecylindrical head 84, which allow the rod 4 to enter the circular orcylindrical cavity 96 of the cylindrical head 84 and rest on top of theslanted seat 86 formed within the circular or cylindrical cavity 94.After the rod 4 is positioned on the slanted seat 86, the slantedstabilizing spacer 88 is received in the cavity 96 such that the tworectangular-shaped end portions 92 are received within the two slots 94,thereby preventing lateral rotation of the spacer 88 within thecylindrical cavity 96. Finally, the outside threaded nut 22 and fixingcap 26 are inserted on top of the slanted spacer 88 to securely hold thespacer 88 and rod 4 within the cylindrical head 84.

FIG. 24 illustrates a perspective view of a marking and guidance device100 for marking a desired location on the spinal pedicle where a pediclescrew 2 will be inserted and guiding the pedicle screw 2 to the markedlocation using a minimally invasive surgical technique. As shown in FIG.24, the marking device 100 includes a tubular hollow guider 52 whichreceives within its hollow an inner trocar 104 having a sharp tip 105 atone end that penetrates a patient's muscle and tissue to reach thespinal pedicle. the inner trocar 104 further includes a trocar grip 106at the other end for easy insertion and removal of the trocar 104. Inone embodiment, the marking and guidance device 100 includes a guiderhandle 108 to allow for easier handling of the device 100.

As shown in FIG. 25, the trocar 104 is in the form of a long tube orcylinder having a diameter smaller than the inner diameter of the hollowof the guider 102 so as to be inserted into the hollow of the tubularguider 102. The trocar 104 further includes a sharp or pointed tip 105for penetrating the vertebral body through the pedicle. The trocar 104further includes a trocar grip 106 having a diameter larger than thediameter of the hollow of the guider tube 102 in order to stop thetrocar 104 from sliding completely through the hollow. The trocar grip106 also allows for easier handling of the trocar 104.

FIGS. 26A and 26B provide perspective views of the marking and guidancedevice 100 after it has been inserted into a patient's back and pushedthrough the muscle and soft tissue to reach a desired location on thespinal pedicle. The desired location is determined using knowntechniques such as x-ray or radiographic imaging for a relatively shortduration of time. After the marking and guidance device 100 has beeninserted, prolonged exposure of the patient to x-ray radiation isunnecessary. As shown in FIG. 26B, after the guidance tube 102 ispositioned over the desired location on the pedicle, the inner trocar104 is removed to allow fiducial pins (not shown) to be inserted intothe hollow of the guidance tube 102 and thereafter be fixed into thepedicle.

FIGS. 27A and 27B illustrate perspective views of two embodiments of thefiducial pins 110 and 112, respectively. As mentioned above, thefiducial pins 110 and 112 according to the present invention areinserted and fixed into the spinal pedicle after passing through thehollow guider 102. The pins 110 and 112 have a cylindrical shape with adiameter smaller than the inner diameter of the hollow of the guidertube 102 in order to pass through the hollow of the guider 102. An endof each fiducial pin is a sharp point 111 configured to be easilyinserted and fixed into the spinal pedicle of the spinal column. In oneembodiment, as shown in FIG. 27B, the other end of the fiducial pinincorporates a threaded shaft 114 which is configured to mate with aninternally threaded tube of a retriever (not shown) for extraction ofthe pin 112. This retriever is described in further detail below withrespect to FIG. 32.

The fiducial pins 110, 112 are preferably made of a durable and rigidbiocompatible metal (e.g., stainless steel, iron steel, titanium,titanium alloy) for easy insertion into the pedicle bone. In contrast toprior art guide wires, because of its comparatively shorter length andmore rigid construction, the fiducial pins 110, 112 are easily driveninto the spinal pedicle without risk of bending or structural failure.As explained above, the process of driving in prior art guidance wireswas often very difficult and time-consuming. The insertion of thefiducial pins 110, 112 into the entry point on the spinal pedicle ismuch easier and convenient for the surgeon and, furthermore, does nothinder subsequent procedures due to a guide wire protruding out of thepatient's back.

FIG. 28 shows a cylindrical pushing trocar 116 having a cylindrical head118 of larger diameter than the body of the pushing trocar 116. Thepushing trocar 116, according to the present invention, is inserted intothe hollow of the guider 102 after the fiducial pin 110 or 112 has beeninserted into the hollow of the guider 102 to drive and fix the fiducialpin 110 or 112 into the spinal pedicle. During this pin insertionprocedure, a doctor strikes the trocar head 118 with a chisel or ahammer to drive the fiducial pin 110 and 112 into the spinal pedicle. Inpreferred embodiments, the pushing trocar 116 is in the form of acylindrical tube, which has a diameter smaller than the inner diameterof the hollow of the guider tube 112. The pushing trocar 116 alsoincludes a cylindrical head 118 having a diameter larger than thediameter of the pushing trocar 116 to allow the doctor to strike it witha chisel or hammer with greater ease. Of course, in alternativeembodiments, a hammer or chisel is not necessarily required. Forexample, depending on the circumstances of each case, a surgeon maychoose to push or tap the head 118 of the pushing trocar 116 with thepalm of his or her hand or other object.

FIG. 29A illustrates how a hammer or mallet 120 and the pushing trocar116 may be used to drive the pin 110, 112 through the hollow of theguider tube 102 and into the designated location of the spinal pedicle.FIG. 29B illustrates a perspective cross-sectional view of the spinalcolumn after two fiducial pins 110, 112 have been driven and fixed intotwo adjacent vertebrae.

After the fiducial pins 110 or 112 have been inserted into the spinalpedicle as discussed above, in one embodiment, a larger hole or areacentered around each pin 110, 112 is created to allow easer insertionand mounting of a pedicle screw 2 into the pedicle bone. The larger holeis created using a cannulated awl 122 as shown in FIG. 30. Thecannulated awl 122 is inserted over the fiducial pin 110, 112 fixed atthe desired position of the spinal pedicle. The awl 122 is in the formof a cylindrical hollow tube wherein an internal diameter of the hollowis larger than the outer diameter of the fiducial pins 110 and 112 sothat the pins 110, 112 may be inserted into the hollow of the awl 122.The awl 122 further includes one or more sharp teeth 124 at a first endfor cutting and grinding tissue and bone so as to create the largerentry point centered around the fiducial pin 110, 112 so that thepedicle screw 2 may be more easily implanted into the spinal pedicle.FIG. 31 illustrates a perspective cross-sectional view of a patient'sspinal column when the cannulated awl 122 is inserted into a minimallyinvasive incision in the patient's back, over a fiducial pin 110, 112 tocreate a larger insertion hole for a pedicle screw 2 (not shown). Asshown in FIG. 31, a retractor 130 has been inserted into the minimallyinvasive incision over the surgical area and a lower tubular body of theretractor 130 is expanded to outwardly push surrounding tissue away fromthe surgical area and provide more space and a visual field for thesurgeon to operate. In order to insert the retractor 130, in oneembodiment, the minimally invasive incision is made in the patient'sback between and connecting the two entry points of the guide tube 102used to insert the two fiducial pins 110, 112. Before the retractor 130is inserted, prior expansion of the minimally invasive incision istypically required using a series of step dilators (not shown), eachsubsequent dilator having a larger diameter than the previous dilator.After the last step dilator is in place, the retractor 130 is insertedwith its lower tubular body in a retracted, non-expanded state. Afterthe retractor 130 is pushed toward the spinal pedicle to a desireddepth, the lower tubular portion is then expanded as shown in FIG. 31.The use of step dilators and retractors are well known in the art.

After the cannulated awl 122 has created a larger insertion hole for thepedicle screw 2, in one embodiment, the fiducial pin 110, 112 isremoved. As discussed above, if the fiducial pin 112 has been used, aretrieving device 140 may be used to remove the fiducial pin 112 beforeimplantation of a pedicle screw 2. As shown in FIG. 32, the retriever140 comprises a long tubular or cylindrical portion having an internallythreaded end 142 configured to mate with the externally threaded topportion 114 of the fiducial pin 112. After the retriever end 142 hasbeen screwed onto the threaded end 114, a doctor my pull the fiducialpin 112 out of the spinal pedicle. In another embodiment, if thefiducial pin 110 without a threaded top portion has been used,appropriate tools (e.g., specially designed needle nose pliers) may beused to pull the pin 110 out.

In alternate embodiments, the fiducial pins 110, 112 are not extractedfrom the spinal pedicle. Instead, a specially designed pedicle screw 144may be inserted into the spinal pedicle over the pin 110, 112 withoutprior removal of the pin 110, 112. As shown in FIG. 33, the speciallydesigned pedicle screw 144 includes an externally threaded shaft 10 anda coupling assembly 14 (FIG. 3) that includes a cylindrical head 16(FIG. 3) for receiving a flexible rod-shaped connection unit 4 (FIGS.4-13). Alternatively, the coupling assembly 14 may be configured toreceive a plate-like connection unit as shown in FIGS. 14-20. Thepedicle screw 144 further includes a longitudinal axial channel (notshown) inside the threaded shaft 10 having an opening 146 at the tip ofthe shaft 10 and configured to receive the fiducial pin 110, 112therein.

FIG. 34 illustrates a perspective cross-sectional view of the patient'sspinal column after a pedicle screw 2 has been inserted into a firstpedicle of the spine using an insertion device 150. Various types ofinsertion devices 150 known in the art may be used to insert the pediclescrew 2. As shown in FIG. 34, after a first pedicle screw 2 has beenimplanted, the retractor 130 is adjusted and moved slightly to providespace and a visual field for insertion of a second pedicle screw at thelocation of the second fiducial pin 110, 112.

FIG. 35 provides a perspective, cross sectional view of the patient'sspinal column after two pedicle screws 2 have been implanted in tworespective adjacent pedicles of the spine, in accordance with thepresent invention. After the pedicle screws 2 are in place, a flexiblerod, plate or hybrid connection unit as described above with respect toFIGS. 4-20 may be connected to the pedicle screws to provide flexiblestabilization of the spine. Thereafter, the retractor 130 is removed andthe minimally invasive incision is closed and/or stitched.

FIG. 36A illustrates a perspective view of a flexible rod 200 for spinalfixation, in accordance with a further embodiment of the invention. Therod 200 is configured to be secured by securing members 2 as describedabove with reference to FIGS. 1-3. In preferred embodiments, the rod200, and rods 210, 220, 230 and 240 described below, are comprised of asolid, cylindrically-shaped rod made of known bio-compatible materialssuch as: stainless steel, iron steel, titanium, titanium alloy, NITINOL,and other suitable metal compositions or materials. As shown in FIG.36A, spiral grooves 202 are cut or formed along at least a portion ofthe length of the cylindrical body of the rod 200. In an exemplaryembodiment, the length of the rod “l” may be between 4 and 8 centimeters(cm), and its cylindrical diameter “D” is between 4-8 millimeters (mm).The spiral grooves 202 have a width “w” between 0.1 and 0.5 mm and aspiral angle θ between 50 and 85 degrees from horizontal. The distancebetween spiral grooves 202 can be between 3 and 6 mm. However, asunderstood by those skilled in the art, the above dimensions areexemplary only and may be varied to achieve desired flexibility, torsionand strength characteristics that are suitable for a particular patientor application.

FIG. 36B illustrates a cross-sectional view of the flexible rod 200,taken along lines B-B of FIG. 36A. As shown, spiral groove 202 is cuttoward the center longitudinal axis of the cylindrical rod 200. Thegroove may be formed continuously in a spiral fashion, as a helix or aninterrupted helix for a solid or hollow rod, or are as disconnectedcircumferential grooves for a solid rod. If hollow rods havedisconnected circumferential grooves formed in them, the grooves canonly partially penetrate the rod material to avoid discontinuities. Inone embodiment, the depth of the groove 202 is approximately equal tothe cylindrical radius of the rod 200, as shown in FIG. 36B, andpenetrates as deep as the center longitudinal axis of the cylindricalrod 200. However, the cross sectional area and shape of the rod, groovedepth, groove width, groove cross-section shape, and groove to groovespacing of the grooved portion of the longitudinal member can be variedto adjust mechanical and structural characteristics as desired. Forexample, deepening or widening grooves increases flexibility, whileincreasing groove-to-groove spacing decreases flexibility. This can beused to modify extent of rod bending at a fixed bending force, customtailor the bent shape of the rod, and equalize mechanical stresses inthe rod during bending in order to minimize material fatigue and improverod reliability.

FIG. 37A illustrates a flexible rod 210 for spinal fixation inaccordance with another embodiment of the invention. The rod 210includes a plurality of transverse holes or tunnels 212 drilled orformed within the body of the rod 210. In one embodiment, the tunnels212 pass through a center longitudinal axis of the cylindrical rod 210at an angle Φ from horizontal. The openings for each respective tunnel212 are located on opposite sides of the cylindrical wall of the rod 210and adjacent tunnels 212 share a common opening on one side of thecylindrical wall, forming a zigzag pattern of interior tunnels 212passing transversely through the central longitudinal axis of the rod210, as shown in FIG. 37A. In one embodiment, the diameter D of eachtunnel 212 may be varied between 0.2 to 3 mm, depending the desiredmechanical and structural characteristics (e.g., flexibility, torsionand strength) of the rod 210. However, it is understood that thesedimensions are exemplary and other diameters D may be desired dependingon the materials used and the desired structural and mechanicalcharacteristics. Similarly, the angle from horizontal Φ may be varied tochange the number of tunnels 212 or the distance between adjacenttunnels 212.

FIG. 37B illustrates a cross-sectional view of the flexible rod 210taken along lines B-B of FIG. 37A. The tunnel 212 cuts through thecenter cylindrical axis of the rod 210 such that openings of the tunnel212 are formed at opposite sides of the cylindrical wall of the rod 210.

FIG. 38A illustrates a perspective view of a flexible rod 220 for spinalfixation, in accordance with a further embodiment of the invention. Rod220 incorporates the spiral grooves 202 described above with referenceto FIGS. 36A and 36B as well as the transverse tunnels 212 describedabove with respect to FIGS. 37A and 37B. The spiral grooves 202 are cutinto the surface of the cylindrical wall of the rod 220 toward a centerlongitudinal axis of the rod 220. As discussed above, the dimensions ofthe spiral grooves 202 and their angle from horizontal θ (FIG. 36A) maybe varied in accordance with desired mechanical and structuralcharacteristics. Similarly, the dimensions of the transverse tunnels 212and their angle from horizontal Φ (FIG. 37A) may be varied in accordancewith desired mechanical and structural characteristics. In oneembodiment, the angles θ and Φ are substantially similar such that theopenings of the tunnels 212 substantially coincide with the spiralgrooves 202 on opposite sides of the cylindrical wall of the rod 220.

FIG. 38B shows a top view of the flexible rod 220 taken along theperspective indicated by lines B-B of FIG. 38A. As shown in FIG. 38B,the openings of the tunnels 212 coincide with the spiral grooves 202. Byproviding both spiral grooves 202 and transverse tunnels 212 within asolid rod 220, many desired mechanical and structural characteristicsthat are suitable for different patients, applications and levels ofspinal fixation may be achieved.

FIG. 39A illustrates a flexible rod 230 for spinal fixation, inaccordance with another embodiment of the invention. The rod 230includes a plurality of transverse tunnels 232 formed in the body of therod 230. The tunnels 232 are substantially similar to the tunnels 212described above with respect to FIGS. 37A and 37B, however, the tunnels232 are not linked together in a zigzag pattern. Rather, each tunnel 232is substantially parallel to its immediate adjacent tunnels 232 and theopenings of one tunnel 232 do not coincide with the openings of adjacenttunnels 232. As shown in FIG. 39A, the angle from horizontal Φ in thisembodiment is approximately 90 degrees. However, it is understood thatother angles Φ may be incorporated in accordance with the presentinvention. It is further understood that the dimensions, size and shapeof the tunnels 232 (as well as tunnels 212) may be varied to achievedesired mechanical and structural characteristics. For example, thecross-sectional shape of the tunnels 212 and 232 need not be circular.Instead, for example, they may be an oval or diamond shape, or otherdesired shape.

FIG. 39B illustrates a cross-sectional view of the rod 230 taken alonglines B-B of FIG. 39A. As shown in FIG. 39B, the transverse tunnel 232travels vertically and transversely through the center longitudinal axisof the rod 230. FIG. 39C illustrates a cross-sectional view of a furtherembodiment of the rod 230, wherein an additional transverse tunnel 232′is formed substantially orthogonal to the first transverse tunnel 232and intersect the first transverse tunnel 232 at the center, cylindricalaxis point. In this way, further flexibility of the rod 230 may beprovided as desired.

FIG. 40A illustrates a perspective view of a flexible rod 240, inaccordance with a further embodiment of the invention. The rod 240includes a plurality of interleaved transverse tunnels 232 and 242 whichare substantially orthogonal to each other and which do not intersect,as shown in FIG. 40A. In another embodiment, a cross-sectional view ofwhich is shown in FIG. 40B, adjacent tunnels 232 and 242 need not beorthogonal to one another. Each tunnel 232, 242 can be offset at adesired angle co from its immediately preceding adjacent tunnel 232,242. As can be verified by those of skill in the art, without undueexperimentation, by varying the dimensions of the tunnels, theirnumbers, and their angular directions with respect to one another,various desired mechanical and structural characteristics for flexiblerods used in spinal fixation devices may be achieved.

Sometimes for multi-level spinal fixation procedures, as shown in FIG.22B for example, it may be desirable for one spinal joint to be rigidlyfixed, while an adjacent spinal joint is dynamically (flexibly)stabilized. An embodiment of a longitudinal member to accomplish thisfunction is shown in FIG. 41A. Axial portion 254 of longitudinal member250 is grooved to provide increased flexibility for bending, whereasaxial portions 252 and 256 are not grooved and remain relatively rigid.The hole 258 is used to terminate the groove to prevent the formation ofcracks and improve reliability. The use of such holes of expandeddiameter to terminate grooves or slots in materials is well known in theart as a means of reducing peak mechanical stresses in materials andreducing the likelihood of material failure.

FIG. 41B illustrates the assembly of the rod 250 of FIG. 41A configuredto be secured to a patient's spine using at least three securing members2 (FIG. 3) having a flexible section 254 disposed between a first pairof securing members 2 and a non-flexible section 252 disposed between asecond pair for securing members 2.

As a further embodiment illustrated in FIG. 41C, an extended ungroovedsection 252 can accommodate a range of positions for a single securingmember 2 to be placed. In another embodiment, extended ungroovedsections can be symmetrically disposed at either end of a groovedsection. It is appreciated that the extended length of section 252provides a “one size fits all” longitudinal member 250 that canaccommodate various distances between the pedicle bones of adjacentvertebrae. As shown in FIG. 41C, the distance between the adjacentsecuring members, 2 and 2′, may be adjusted by selecting the location ofthe securing member 2 on section 252. Any excess length of section 252can then be trimmed away or removed.

Groove parameters such as groove depth, groove width, groovecross-section shape or profile, and groove to groove spacing of thegrooved portion 254 can be uniformly constant for uniform structural andmechanical characteristics along the axis of the grooved portion 254.Sometimes it is advantageous to have axially varying structural andmechanical characteristics for the longitudinal member in order tocontrol local mechanical stress levels, custom tailor bending shapes, oraffect resistance to bending in all bending directions or in selectedbending directions. The cross-sectional area of a cylindrical (forexample) hollow longitudinal member can be changed by changing the outerdiameter, while maintaining constant wall thickness for the hollowcylinder. Another embodiment is to modify the wall thickness byadjusting the internal diameter (i.e. the diameter of the cavity withinthe cylinder) while keeping the outer diameter of the hollow cylinderconstant. Still other embodiments simultaneously vary the externaldiameter and the internal diameter. It is easily seen how the abovearguments also apply to longitudinal members with shapes that are notcylindrical.

FIG. 42A illustrates a side view of a flexible, spirally groovedstabilization device 270 in accordance with an embodiment of theinvention. The spirally grooved section 271 has an expanded outerdiameter relative to ungrooved sections 262 and 262′. Whereas the spiralgroove imparts increased flexibility to section 271, it would alsoimpart greater per unit area material strain to section 271 relative toungrooved sections 262 and 262′ because of reduced cross-sectionalmaterial area in section 271, due to the presence of the grooves, if theouter diameter of spirally grooved section 271 were the same as theouter diameter of the ungrooved sections 262 and 262′. Expanding theouter diameter of section 271 can maintain acceptable material stresslevels during the flexing of the spirally grooved section 271 for boththe spirally grooved section 271, and the ungrooved sections 262 and262′.

In one embodiment, if the longitudinal member of FIG. 42A is hollow, theinner diameter of the cavity of the spirally grooved section 271 can bethe same as the inner diameter of the cavity of the ungrooved sections262 and 262′, whereas the outer diameter of the grooved flexible section271 is increased to reduce material stresses during bending and/or varythe flexibility of the grooved section 271.

FIGS. 42A and 42B (discussed below) illustrate examples of alongitudinal spinal stabilization device wherein a flexible section hasa different cross-sectional profile (e.g., outer diameter (in the caseof a cylindrical rod) or perimetric shape) than that of correspondingend portions of the longitudinal stabilization device.

In a further embodiment, the cross-sectional profile (e.g., outerdiameter) of the grooved flexible section is kept the same as thecross-sectional profile (e.g., outer diameter) of the ungroovedsections, whereas the inner diameter of the cavity of the groovedflexible section is reduced relative to the inner diameters of thecavities of the ungrooved sections. This has a similar material stressreduction effect as described above.

In still further embodiments of the present invention, both inner andouter diameters of the grooved flexible section can be varied withrespect to the inner and outer diameters of the ungrooved sections toreduce material strain differences between the sections.

FIG. 42B illustrates a side view of another embodiment of the presentinvention that accomplishes variation in flexibility along alongitudinal axis by adjusting the cylindrical diameter orcross-sectional profile of the grooved section 266 (while maintaining aconstant inner cavity diameter for the case of a hollow longitudinalmember) in order to achieve reduced mechanical stresses in the vicinityof transition sections 264 and 264′, between the grooved section 266 andungrooved sections 262 and 262′, respectively. The outer diameter of thegrooved section 266 is smallest near a central portion of the groovedsection 266 and gradually expands toward the ungrooved sections 262.This provides more cross-sectional material area to distribute forcesthrough, thereby reducing per unit area stress in the regions of thegrooved section 266 near the transition sections 264 and 264′.

In another embodiment, axial variations of groove depth, groove width,groove cross-section shape, and groove to groove spacing can alsoachieve axially variant flexibility and mechanical characteristics,either alone or in combination with variance of the cylindricalcross-section as discussed above. For example: (i) tapering the groovedepth from a maximum near the center of a grooved section to near zeroat a boundary with a non grooved section (FIG. 43A); (ii) tapering thegroove width from a maximum near the center of a grooved section to nearzero at a boundary with a non grooved section (FIG. 43B); (iii)transitioning groove shape from one permitting maximum flexure near thecenter of a grooved section to a shape providing reduced flexure at aboundary with a non grooved section (FIG. 43C); or (iv) expanding grooveto groove spacing from a minimum near the center of a grooved section toa maximum at a boundary with a non grooved section (FIG. 43D).

FIG. 44 illustrates a longitudinal member with an elastomer cladding 278around the grooved section 276. In this embodiment, elastomer cladding278 covers only grooved section 276 and does not cover ungroovedsections 272. Also optional tapers 274 are formed in the longitudinalmember to provide for a smooth surface transition between clad andunclad sections. These optional tapers 274 also fixate the longitudinalposition of the cladding. Alternately the cladding may be extended ontoan ungrooved section 272. The elastomer cladding may (i) contact onlythe surface of the longitudinal member, (2) additionally penetrate intothe groves of the longitudinal member, or (3) if the longitudinal memberis hollow, additionally penetrate to and at least partially fill theinside of the longitudinal member. The elastomer cladding providesadditional control over the axial and flexural stability of thelongitudinal member, as well as providing a barrier between tissues andthe grooved section.

The elastomer cladding can consist of any of a variety of medical gradeelastomers, including, for example, silicone, polyurethane,polycarbonateurethane and silicone-urethane copolymers. The cladding canbe applied to the longitudinal member using a variety of techniques thatare well known in the art. In one technique, a thermoplastic orthermosetting resin can be injected into a heated mold surrounding thedesired section of the longitudinal member, while it is affixed within amold. An advantage of this injection molding process is that it canaccommodate cladding material that are not of sufficiently low viscosityfor application by alternate means at room temperature and pressure. Afurther advantage of injection molding is that the shape of the exteriorof the cladding is determined by the shape of the mold that is used.Another injection molding advantage is the reproducible penetration ofgroove interstices and the interior of hollow longitudinal members.Alternative molding techniques include compression molding and transfermolding,

Other cladding application methods include liquid injection molding,dipping, spraying, or painting with a mechanical applicator such as apaintbrush. These methods require that the cladding material be appliedin a low viscosity form. For an example a resin for application could besuspended in a solvent that evaporates after application. In anotherexample, the cladding material is applied in a low viscosity form andsubsequently cured through chemical, heat, or radiation methods. It issometime useful to mask parts of the longitudinal member whereapplication of the cladding material is not desired.

FIG. 45A illustrates a uniform cross-section of a rod as the flexiblesection of a longitudinal member made of a material 277. FIG. 44Billustrates a non-uniform cross-section of a rod as a flexible sectionof a longitudinal member made of a material 277, that includes a sectionmade of another material 279. Clearly the rod of FIG. 45A will exhibitthe same bending behavior with applied force in both the x and ydirections. If the materials of sections 320 and 330 have differentbending characteristics, the rod of FIG. 45B will exhibit differentbending behavior with applied force for the x and y directions. Forexample, if material 279 in FIG. 45B is stiffer than material 277, therod will bend more easily in the x direction than in the y direction.

Various embodiments of the invention have been described above. However,those of ordinary skill in the art will appreciate that the abovedescriptions of the preferred embodiments are exemplary only and thatthe invention may be practiced with modifications or variations of thedevices and techniques disclosed above. Those of ordinary skill in theart will know, or be able to ascertain using no more than routineexperimentation, many equivalents to the specific embodiments of theinvention described herein. Such modifications, variations andequivalents are contemplated to be within the spirit and scope of thepresent invention as set forth in the claims below.

1. A connection unit for use in a spinal stabilization device comprisinga longitudinal member configured to be secured to a patient's spineusing at least three securing members; wherein a first section of thelongitudinal member, configured to be positioned between a first pair ofsecuring members, exhibits greater flexibility than a second section ofthe longitudinal member, configured to be positioned between a secondpair of securing members.
 2. The connection unit of claim 1 wherein thelongitudinal member is configured in the shape of a cylindrical rod. 3.The connection unit of claim 1 wherein the first section comprises atleast one groove formed therein for providing flexibility to the firstsection.
 4. The connection unit of claim 3 wherein the at least onegroove is a spiral groove.
 5. The connection unit of claim 3 wherein theat least one groove terminates on a strain relief hole of a largerdiameter than the groove width.
 6. The connection unit of claim 1wherein the longitudinal member comprises a material selected from agroup of known, bio-compatible materials consisting of metals, metalalloys, organic polymers, naturally occurring resins, thermoplastics,elastomers and composite materials.
 7. The connection unit of claim 3wherein the longitudinal member comprises a solid object.
 8. Theconnection unit of claim 3 wherein the longitudinal member comprises ahollow object.
 9. The connection unit of claim 3 wherein thelongitudinal member comprises a hollow object of a first material thatis at least partially filled with a second material, the second materialcomprising one of a group of known, bio-compatible materials consistingof organic polymers, naturally occurring resins, elastomers andcomposite materials.
 10. A connection unit for use in a spinalstabilization device comprising a longitudinal member comprising firstand second ends, and a flexible section disposed between the first andsecond ends, the flexible section having at least one groove formedtherein, wherein the flexible section is characterized by across-sectional profile that is different from that of the first andsecond ends.
 11. The connection unit of claim 10 wherein thelongitudinal member is configured in the shape of a cylindrical rod. 12.The connection unit of claim 10 wherein a cross-sectional profile of theflexible section is smaller than a cross sectional profile of at leastone of the first or second ends, thereby providing increased flexibilityto the flexible section.
 13. The connection unit of claim 10 wherein thecross-sectional profile of the flexible section is greater than a crosssectional profile of at least one of the first or second ends.
 14. Theconnection unit of claim 10 wherein the cross-sectional profile of theflexible section is tapered along a longitudinal axis of the flexiblesection such that a cross-sectional profile of the flexible section issmallest near a central portion of the flexible section and is largestat opposing transition sections between the flexible section andopposing first and second ends.
 15. The connection unit of claim 10wherein the longitudinal member comprises a first material selected froma group of known, bio-compatible materials consisting of metals, metalalloys, organic polymers, naturally occurring resins, thermoplastics,elastomers and composite materials.
 16. The connection unit of claim 10,wherein the flexible section comprises a hollow object of a firstmaterial that is filled with a second material, the second materialcomprising one of a group of known, bio-compatible materials consistingof organic polymers, naturally occurring resins, elastomers andcomposite materials.
 17. The connection unit of claim 16 wherein thesecond material decreases the compressibility of the flexible sectiondue to an applied load.
 18. The connection unit of claim 16 wherein thesecond material is more flexible than the first material and increasesthe energy absorption of the flexible section for a given deflection.19. The connection unit of claim 16, wherein the second material hasdifferent flexibility from the first material, and the second material'scross-section is non-uniformly distributed along an axis of thelongitudinal member to provide different flexibility in differentbending directions.
 20. A connection unit for use in a spinalstabilization device comprising a longitudinal member having alongitudinal axis, first and second ends configured to be secured to apatient's spine using respective securing members, and a flexiblesection between the first and second ends, wherein the flexible sectionhas at least one groove formed therein, and wherein at least one grooveparameter varies along at least a portion of the longitudinal axis ofthe flexible section.
 21. The connection unit of claim 20 wherein thelongitudinal member is configured in the shape of a cylindrical rod. 22.The connection unit of claim 20 wherein the longitudinal membercomprises a first material selected from a group of known,bio-compatible materials consisting of metals, metal alloys, organicpolymers, naturally occurring resins, thermoplastics, elastomers andcomposite materials.
 23. The connection unit of claim 20 wherein the atleast one groove parameter comprises the width of the groove along thelongitudinal axis of the connection unit.
 24. The connection unit ofclaim 20 wherein the at least one groove parameter comprises across-sectional depth of the groove.
 25. The connection unit of claim 20wherein the at least one groove parameter comprises a groove-to-groovespacing.
 26. The connection unit of claim 20 wherein the at least onegroove comprises a circumferential spiral along the longitudinal axis.27. The connection unit of claim 20 wherein the at least one groovecomprises a first groove and a second groove, and wherein the firstgroove is not contiguous with the second groove.
 28. The connection unitof claim 20 wherein the at least one groove terminates on a strainrelief hole of a larger diameter than the groove width.
 29. A connectionunit of a first material for use in a spinal stabilization devicecomprising a longitudinal member having first and second ends,configured to be secured to a patient's spine using respective securingmembers, and a flexible section in between the first and second endswherein at least part of the flexible section is clad with a cladding ofa second material.
 30. The connection unit of claim 29 wherein thelongitudinal member is configured in the shape of a cylindrical rod. 31.The connection unit of claim 29 wherein the first material comprises amaterial selected from a group of known bio-compatible materialsconsisting of metals, metal alloys, organic polymers, naturallyoccurring resins, thermoplastics, elastomers and composite materials.32. The connection unit of claim 29 wherein the second materialcomprises a material selected from a group of known bio-compatiblematerials consisting of organic polymers, elastomers, naturallyoccurring resins, and composite materials.
 33. The connection unit ofclaim 29 wherein the cladding is injection molded around thelongitudinal member.
 34. The connection unit of claim 29 wherein thecladding is applied to the longitudinal member by dipping thelongitudinal member.
 35. The connection unit of claim 29 wherein thecladding is applied to the longitudinal member by spraying thelongitudinal member.
 36. The connection unit of claim 29 wherein thecladding is applied to the longitudinal member with a mechanicalapplicator.
 37. The connection unit of claim 29 wherein the cladding isa separately manufactured part that is conformable with a centralsection of modified flexibility, and is assembled with the longitudinalmember.
 38. A connection unit for use in a spinal stabilization devicecomprising a longitudinal member having first and second ends, with aflexible section disposed in between the first and second ends, whereinat least one of the first or second ends is of a sufficient length toaccommodate a range of positions for coupling to a securing member. 39.The connection unit of claim 38 wherein the longitudinal member isconfigured in the shape of a cylindrical rod.
 40. The connection unit ofclaim 38 wherein the at least one end may be cut to length to remove alength of material that extends beyond a securing member.
 41. Theconnection unit of claim 38 wherein only one end is of sufficient lengthto accommodate a range of positions for coupling to a securing member,such that a wide range of positions for coupling to a securing membermay be achieved with a connection unit of one size with no more than oneoperation to cut the connection unit to length.
 42. The connection unitof claim 38 wherein the flexible section comprises at least one groove.43. The connection unit of claim 38 wherein the groove is a spiralgroove.
 44. The connection unit of claim 38 wherein the longitudinalmember comprises a material selected from a group of knownbio-compatible materials consisting of metals, metal alloys, organicpolymers, naturally occurring resins, thermoplastics, elastomers andcomposite materials.